1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a manufacturing method of an array substrate for a transflective liquid crystal display (LCD) device.
2. Discussion of the Related Art
In general, the liquid crystal display (LCD) device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode and the electrodes of each substrate are also facing each other. Voltage is applied to each electrode and an electric field is induced between the electrodes. An arrangement of the liquid crystal molecules is changed by varying intensity of the electric field. The LCD device displays a picture by varying transmittance of the light intensity according to the arrangement of the liquid crystal molecules.
Because the liquid crystal display (LCD) device is not luminescent, it needs an additional light source in order to display images. The liquid crystal display device is categorized into a transmissive type and a reflective type depending on the kind of light source.
In the transmissive type, a backlight behind a liquid crystal panel is used as a light source. Light incident from the backlight penetrates the liquid crystal panel, and the amount of the transmitted light is controlled depending on the arrangement of the liquid crystal molecules. Here, the substrates are usually transparent and the electrodes of each substrate are usually formed of transparent conductive material. As the transmissive liquid crystal display (LCD) device uses the backlight as a light source, it can display a bright image in dark surroundings. Because an amount of the transmitted light is very small for the light incident from the backlight, the brightness of the backlight must be increased in order to increase the brightness of the LCD device. Consequently, the transmissive liquid crystal display (LCD) device has high power consumption due to the operation of the backlight.
On the other hand, in the reflective type LCD device, sunlight or artificial light is used as a light source of the LCD device. The light incident from the outside is reflected at a reflective plate of the LCD device according to the arrangement of the liquid crystal molecules. Since there is no backlight, the reflective type LCD device has much lower power consumption than the transmissive type LCD device. However, the reflective type LCD device cannot be used in dark surroundings because it depends on an external light source.
Therefore, a transflective LCD device, which can be used both in a transmissive mode and in a reflective mode, has been recently proposed. A related art transflective LCD device will be described hereinafter more in detail.
FIG. 1 is an exploded perspective view illustrating a related art transflective LCD device. The related art transflective LCD device 11 has upper and lower substrates 15 and 21, which are spaced apart from and facing each other, and also has a liquid crystal layer 14 interposed between the upper substrate 15 and the lower substrate 21.
A gate line 25 and a data line 39 are formed on the inner surface of the lower substrate 21. The gate line 25 and the date line 39 cross each other to define a pixel area “P”. The pixel area“P” includes a transmissive region “A” and a reflective region “B”. A thin film transistor “T” is situated at the crossing of the gate line 25 and the data line 39. A reflective electrode 49 having a transmissive hole 49a and a transparent electrode 61 overlapping the reflective electrode 49 are formed in the pixel area “P”. The reflective electrode 49 and the transparent electrode 61 are connected to the thin film transistor “T”. The transmissive hole 49a corresponds to the transmissive region “A”.
Meanwhile, a black matrix 16, which has an opening corresponding to the reflective electrode 49 and the transparent electrode 61, is formed on the inside of the upper substrate 15, and a color filter 17 corresponding to the opening of the black matrix 16 is formed on the black matrix 16. The color filter 17 is composed of three colors: red (R), green (G) and blue (B). Each color corresponds to each pixel area “P”. Subsequently, a common electrode 13 is formed on the color filter 17.
FIG. 2 is a schematic cross-sectional view of a related art transflective LCD device. FIG. 2 indicates a pixel area of the related art transflective LCD device. In the related art transflective LCD device 11, a transparent electrode 61 is formed on the inner surface of a lower substrate 21 and an insulating layer 50 is formed on the transparent electrode 61. A reflective electrode 49 is formed on the insulating layer 50, and the reflective electrode 49 has a transmissive hole 49a corresponding to a transmissive region “A”. As stated above, the lower substrate 21 includes a gate line, a data line and a transistor thereon though not shown in the figure.
An upper substrate 15 is spaced apart from and facing the lower substrate 21. A common electrode 13 is formed on the inner surface of the upper substrate 15. Though not shown in the figure, a black matrix and a color filter are subsequently formed between the upper substrate 15 and the common electrode 13.
A liquid crystal layer 14 is disposed between the lower and upper substrates 21 and 15, and molecules of the liquid crystal layer 14 are arranged horizontally with respect to the substrates 21 and 15.
Polarizers (not shown) are arranged on the outer surface of the lower and upper substrate 21 and 15. The transmission axes of polarizers are perpendicular to each other.
A backlight 41 is located under the outside of the lower substrate 21. The backlight 41 is used as a light source of a transmissive mode of the transflective LCD device.
In a reflective mode, light “F2” incident from the outside such as sunlight or artificial light passes through the liquid crystal layer 14 and is reflected at the reflective electrode 49 in a reflective region “B”. The light “F2” goes through the liquid crystal layer 14 again and is emitted. At this time, the amount of emitted light “F2” is controlled according the arrangement of liquid crystal molecules.
On the other hand, in a transmissive mode, light “F1” from the back light 41 penetrates the transparent electrode 61 in the transmissive region “A”. Next, while the light “F1” passes through the liquid crystal layer 14, the amount of the light “F1” is controlled according to the arrangement of liquid crystal molecules.
FIG. 3 shows a plan view of an array substrate for a related art transflective liquid crystal display (LCD) device. In FIG. 3, a gate line 25 is formed horizontally and a data line 39 is formed vertically in the context of the figure. The gate and data lines 25 and 39 cross each other and define a pixel region “P”. At the crossing of the gate and data lines 25 and 39, a thin film transistor “T” is formed. The thin film transistor “T” is electrically connected to the gate and data lines 25 and 39, and includes a gate electrode 23, a source electrode 35, a drain electrode 37, and an active layer 31.
In the pixel region “P”, a reflective electrode 49 and a transparent electrode 61 are formed. The reflective electrode 49 has a transmissive hole 49a. The transparent electrode 61 overlaps the drain electrode 37 and is connected to the drain electrode 37 through a drain contact hole 53.
A capacitor electrode 43, which overlaps the gate line 25, is formed and is connected to the transparent electrode 61 through a capacitor contact hole 55. The capacitor electrode 43 forms a storage capacitor “C” with the gate line 25.
A gate pad 27 is formed at one end of the gate line 25 and a data pad 41 is formed at one end of the data line 39. A gate pad terminal 63 and a data pad terminal 65, which overlap the gate pad 27 and the data pad 41, respectively, are formed. The gate pad 27 is connected to the gate pad terminal 63 through a gate pad contact hole 57 and the data pad 41 is connected to the data pad terminal 65 through a data pad contact hole 59.
FIGS. 4A to 4F are cross-sectional views illustrating a method of manufacturing the array substrate of FIG. 3, and correspond to cross-sections along the line IV—IV of FIG. 3.
First, as shown in FIG. 4A, a gate electrode 23, a gate line 25 and a gate pad 27 are formed on a substrate 21. As stated above, the gate pad 27 is formed at one end of the gate line 25. A gate insulator 29 is formed on the gate electrode 23, the gate line 25 and the gate pad 27. Next, an active layer 31 and an ohmic contact layer 33 are subsequently formed on the gate insulator 29. The active layer 31 and the ohmic contact layer 33 are disposed over the gate electrode 23.
A data line 39, source and drain electrodes 35 and 37 are formed on the ohmic contact layer 33. Also, a capacitor electrode 43 and a data pad 41 are formed on the gate insulator 29. As stated above, the data line 39 crosses the gate line 25 to define a pixel region “P”. The capacitor electrode 43 and a data pad 41 are made of substantially the same material as the source and drain electrodes 35 and 37. The source and drain electrodes 35 and 37 form a thin film transistor “T” with the gate electrode 23. The capacitor electrode 43 overlaps the gate line 25 to form a storage capacitor.
In FIG. 4B, a first passivation layer 45 is formed on the source and drain electrodes 35 and 37, the capacitor electrode 43, and the data pad 41. Next, a second passivation layer 47 is formed on the first passivation layer 45. The first passivation layer 45 is made of an inorganic material such as silicon nitride (SiNx) or silicon oxide (SiO2). The second passivation layer 47 is made of an organic material such as benzocyclobutene (BCB) or acrylic resin. The second passivation layer 47 flattens the surface of the substrate 21 having the thin film transistor “T” and minimizes electrical couplings between the gate line or the data line and the reflector, which will be formed later.
As shown in FIG. 4C, the second passivation layer 47, the first passivation layer 45 and the gate insulator 29 are patterned and a first transmissive hole 48 is formed. Accordingly, the substrate 21 is exposed. The presence of the first transmissive hole 48 causes a thickness of a liquid crystal layer in a transmissive region to be thicker than that of a liquid crystal layer in a reflective region, and optimizes the optical characteristic of a transmissive mode with the optical characteristic of a reflective mode, simultaneously.
Next, in FIG. 4D, a reflector 49 is formed on the second passivation layer 47 and a third passivation layer 51 is formed on the reflector 49. The reflector 49 has a second transmissive hole 49a corresponding to the first transmissive hole 48. The reflector 49 is made of a metal that reflects light well, such as aluminum (Al). The reflector 49 may be formed of either aluminum (Al) or an alloy of aluminum and neodymium (AlNd). The third passivation layer 51 is made of an inorganic material.
In FIG. 4E, the third passivation layer 51 is patterned with the second passivation layer 47, the first passivation layer 45 and the gate insulator 29, so that a drain contact hole 53, a capacitor contact hole 55, a gate pad contact hole 57 and a data pad contact hole 59 are formed. A third transmissive hole 52 is also formed and the third transmissive hole 52 corresponds to the first and second transmissive holes 48 and 49a. The drain contact hole 53 exposes the drain electrode 37, the capacitor contact hole 55 exposes the capacitor electrode 42, the gate pad contact hole 57 exposes the gate pad 27, and the data pad contact hole 59 exposes the data pad 41. The drain, capacitor, gate pad and data pad contact holes 53, 55, 57 and 59 may have a taper, a lower width of which is narrower than an upper width.
As shown in FIG. 4F, a transparent electrode 61, a gate pad terminal 63 and a data pad terminal 65 are formed. The transparent electrode 61 is connected to the drain electrode 37 and the capacitor electrode 43 through the drain and capacitor contact holes 53 and 55, respectively. The gate and data pad terminals 63 and 65 are connected to the gate and data pads 27 and 41 through the gate and data pad contact holes 57 and 59, respectively.
FIG. 5 is a cross-sectional view magnifying the gate pad area “D” of FIG. 4F. In the above method of manufacturing an array substrate for a transflective LCD device, the gate insulator 29 and the first to third passivation layers 45, 47 and 51 are etched one at a time in order to form the contact holes 53, 55, 57 and 59. The etch rate of each layer is not equal to each other because of various constituent materials, i.e., an organic material and an inorganic material. Therefore, the contact holes 53, 55, 57 and 59 have a reverse taper shape in parts “E” due to the different etching rates of the organic material and the inorganic material. Accordingly, the transparent electrode 61 can become disconnected between the organic material and inorganic material in the vicinity of the reverse taper shape.
Additionally, since most of the layers are etched, including the gate insulator 29, and the first to third passivation layers 45, 47 and 51, in order to form the gate pad contact hole 57 exposing the gate pad 27, a photoresist layer (not shown), which protects remaining parts during the etch process, is not remained in the vicinity of the parts E. Therefore, the layers are etched in areas not to be etched. To solve the problems, the photoresist layer should have a thickness of about 3.3 μm, but the photoresist usually has a thickness of about 2.7 μm. Accordingly, the margin of the photoresist layer is small and the size of the third contact hole 57 changes.
The drain and capacitor contact holes 53 and 55, the transmissive hole 48, and data pad contact hole 59 are over-etched during the etch process in the vicinity of parts E.